Field devices, such as, for example, a measuring transducer, are applied widely in process and automation technology. The field devices serve for registering and/or influencing process variables. Serving for registering process variables are measuring devices, such as, for example, a measuring transducer for pressure, which registers the corresponding process variable, pressure. For influencing process variables, actuators are used, such as valves or pumps, via which e.g. the pressure in a line or in a container is changed.
In situations, in which an error occurs in the registering of a process variable, it can happen that due to this error the influencing of the process variable happens defectively. For example, if a measuring transducer registers a pressure defectively, so that a pressure measurement value is ascertained, which corresponds to a pressure, which is lower than an actual pressure in a container, it can happen that a control unit connected with the pressure measuring transducer and with a pump so controls a pump via a control system that the pressure in the container is still further increased. Such an error can possibly cause considerable damage.
In the case of pressure measuring devices, respectively transducers for measuring pressure, there are in some applications requirements relative to cleanliness. The field devices, which are applied, for example, in a yogurt factory, must be so cleaned that hygienic requirements are fulfilled. Among other things, this means that the pressure measuring devices are cleaned in a specified manner. In the course of this, the opening of the reference pressure supply in the wall of the housing of a relative pressure measuring transducer must be protected against the penetration of water, for example, during a cleaning procedure. If water or other material penetrates into the reference pressure supply, it can lead to errors in the registering of the pressure.
It is known, for example from German Patent, DE 20 2011 108 899 U1, to incorporate a (polytetrafluorothylene) PTFE membrane into the reference pressure supply. This enables the penetration of air but blocks liquids.
Pressure measuring devices are applied under varied conditions. Among other things, this means that the spatial orientation, in which the measuring device will be mounted, is not known at the time of fabrication of the measuring device. Therefore, it can occur that an installed PTFE membrane has a recess or forms a pocket with the housing wall. When the measuring device or the measuring transducer is then so mounted that water can collect in this recess, this can likewise lead to an error in the registering of the pressure.